I'm not sure about ones in Seattle, but over in Bellevue the IHOP closes at 10pm weekdays, Midnight on weekends. As far as I know, there's practically nothing open after 10pm on the Eastside. Burgermaster stays open to Midnight (1AM Friday / Saturday), but beyond that I don't know of anything besides fast food or Denny's/Shari's type places that stay open late, much less 24 hours.

Minnie's is closed down, and Dicks is only open until 2am. If you're hunting for super late night food on Friday or Saturday, I know Ga Ga Loc in the ID (king and maynerd?) is usually open until 4am. not much else is edible at this hour, subway in the U-district? that's 24 hours and probably won't kill you.